1. Field of the Invention
The invention disclosed in this specification and the like relates to a display device and a method for manufacturing the display device. One embodiment of the present invention particularly relates to a display device having a transistor including an oxide semiconductor film and a method for manufacturing the display device.
2. Description of the Related Art
Since display devices using light-emitting elements such as organic electroluminescence (hereinafter, also referred to as EL) have high visibility, are suitable for reduction in thickness, and do not have limitations on viewing angles, they have attracted attention as display devices which can take the place of cathode ray tubes (CRTs) or liquid crystal display devices. In an active matrix display device using a light-emitting element, in general, at least a light-emitting element, a transistor (a switching (selection) transistor) which controls input of a video signal to a pixel, and a transistor (a driving transistor) which controls a value of current supplied to the light-emitting element are provided in each pixel.
Transistors used for display devices are formed using silicon semiconductors such as amorphous silicon, single crystal silicon, and polycrystalline silicon provided over glass substrates.
In recent years, instead of the silicon semiconductor, a technique in which a metal oxide having semiconductor characteristics (an oxide semiconductor) is used for transistors has attracted attention. For example, a technique is disclosed in which a transistor is manufactured using zinc oxide or an In—Ga—Zn oxide as an oxide semiconductor and the transistor is used as a switching transistor or the like of a pixel of a display device (see Patent Document 1).